This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our research efforts are focused on the structure of human La NTD protein-RNA complex to define the molecular basis for binding affinity and specificity of La autoantigen targeted to the 3-end of nascent RNA transcripts. We have used NMR spectral quality to screen a series of RNA oligomers terminating with UUUOH 3-ends for their ability to form complexes with La NTD in solution. The best NMR spectra were found for complexes of La NTD with the UUUOH 3-mer and 9-mer RNA oligomers containing 3-UUUOH ends, with the later yielding diffraction quality crystals. The crystals belong to space group P21212 with two complex molecules per asymmetric unit and diffracted to 2.9 A at home X-ray source. Partial structure solution has been found by molecular replacement method using x-ray data collected from native crystal at 19ID beamline at APS. We have crystallized complex with selenomethionine (SeMet) protein to obtain experimental phases for structure determination. Our long-term goal is to investigate basis of RNA recognition by the individual NTD and CTD as well as full-length La protein.